Red phenyl-azo-naphthol dyestuffs for edible compositions



United States Patent Ofhce 3,519,617 Patented July 7, 1970 3,519,617 REDPHENYL-AZO-NAPHTHOL DYESTUFFS FOR EDIBLE COMPOSITIONS Gustav E. Rast,Hamburg, and Russell I. Steiner, Williamsville, N.Y., assignors toAllied Chemical Corporation, New York, N.Y., a corporation of New YorkNo Drawing. Filed May 18, 1967, Ser. No. 639,264 Int. Cl. C07c 107/08;A23] 1/ 27 US. Cl. 260-200 9 Claims ABSTRACT OF THE DISCLOSURE Thisinvention relates to the production of novel red monoazo dyestuffs. Moreparticularly, the present invention is directed to highly soluble redmonoazo dyestuffs and to their use as colorants, especially in dyeing ofedible substrates.

Certain red dyes have found use in the past in various coloring ordyeing applications, especially in the coloring of foodstuffs or otheredible substrates. One such dyestuff F.D. & C. Red No. 4) recently hasbeen delisted for essentially all edible uses by the Food and DrugAdministration, thereby creating a need for a red dye particularlyuseful in the coloring of edible substrates.

Accordingly, one object of the present invention is to provide new anduseful dye compositions.

A further object of the present invention is to provide highly solublenon-toxic monoazo dye compositions which are useful in the coloring ofedible substrates.

Other objects of this invention will be readily apparent to thoseskilled in the art from the following description.

The monoazo dyestuffs of the present invention correspond to theformula:

wherein R and R are each lower alkyl containing from 1 to 6 carbon atomsand M is hydrogen, ammonium or a physiologically acceptable metalcation, such as sodium, potassium, barium calcium and iron. Preferreddyestuffs of the present invention are compounds conforming to aboveFormula I wherein R and R are each methyl and M is sodium, potassium orammonium because of the particularly low toxicity and high watersolubility of such compounds; most preferred of the compounds of thepresent invention is the disodium salt of l-([6-methoxy-4-sulfo-m-tolyl]azo)-2-naphthol-6-sulfonic acid. It is to beunderstood that mixed salts, such as the rnonosodium, monopotassiumsalts, as well as acid salts are contemplated as being within thepresent invention. Representative compounds of the present inventionother than the aforementioned disodium salt include:

1-( [6-methoxy-4-sulfo-m-tolyl] azo) -2-naphthol- 6,6-sulf0nic acid l-([6-methoxy-4-sodiumsulfo-m-tolyl] azo -2-naphthol- 6-sulfonic aciddipotassium salt of 1-([6-methoxy-4-sulfo-m-tolyl]azo)-2-naphthol-6-sulfonic acid diammonium salt ofl-([6-methoxy-4-sulfo-m-tolyl]azo)- 2-naphthol-6-sulfonic acid calciumsalt of 1-([6-methoxy-4-sulfo-m-tolyl]azo)- 2-naphthol-6-sulfonic acidbarium salt of 1-([6-meth0xy-4-sulfo-m-tolyl]azo)- 2-naphthol-6-sulfonicacid ferrous salt of l-([6-methoxy-4-sulfo-m-tolyl]azo)-2-naphthol-6-sulfonic acid disodium salt of1-([6-ethoxy-4-sulfo-m-tolyl]azo)- 2-naphthol-6-sulfonic acid disodiumsalt of 1( [6-propoxy-4-sulfo-m-tolyl]azo)- 2-naphthol-6-sulfonic aciddisodium salt of 1([2-methoxy-5-ethyl-4-sulfophenyl] azo-2-naphthol-6-sulfonic acid disodium salt of 1-([Z-ethoxy-5-ethyl-4-sulfophenyl]azo)- 2-naphthol-6-sulfonic aciddisodium salt of 1-([2-propoxy-5-propyl-4-sulfophenyl] azo-2-naphthol-6-sulfonic acid As previously indicated, the dyestuffs ofthe present invention are essentially non-toxic to warm blooded animalsand are sufficiently soluble in water to meet the requirements of theFood and Drug Administration as to tolerances governing dye content. Forexample, the disodium salt of 1-( [6-methoxy-4-sulfo-m-tolyl]azo)-2-naphthol-6- sulfonic acid, one of the preferred dyes of the presentinvention, is soluble to the extent of about 18 parts per parts of Waterat 2 C. Further, these dyestuffs are stable to sulfur dioxide in aqueoussolutions, to hydrogen ions in aqueous solutions having a pH of 3 orhigher, to ascorbic acid in concentrations ranging from about 50 to 100ppm, which are commonly encountered in food preparations, as well as toheat such as that encountered in baking operations, e.g., C. for 25minutes. Additionally, when used to color soft drinks, these dyestuffsprovide compositions which are essentially non-corrosive to beveragecontainers for periods of at least six months. The novel dyestuffs alsopossess excellent light stability in a variety of edible substrata andexhibit excellent retentive properties when contacted with suchsubstrata.

These characteristics of the red monoazo dyestuffs of the presentinvention are indicative of their suitability as colorants for ediblesubstrata, e.g., fruits, such as cherries; sugar pattie; hard candies;gelatine deserts; soft drinks, both carbonated and uncarbonated; cakeand cookie prepared mixes; as Well as wrappings and printed labelswhich, in use, come in contact with these and other food compositions.These characteristics together with their extremely low toxicity to warmblooded animals, as determined by both acute and chronic feeding tests,indicate their value as an addition to the list of dyestuffs certifiableby the United States Government Food and Drug Administration. Forexample, acute feeding tests using the disodium salt of 1-([6-methoxy-4-sulfo-m-tolyl] azo)-2-naphthol-6-sulfonic acid havedemonstrated that animals tolerate high levels of this dyestuff whilechronic feeding tests involving additions of up to 5.0%, by weight, ofthis dyestuff to normal rations indicated no significant changes in thegrowth rate and food consumption of rats as compared with a controlgroup studied simultaneously.

Examplary of the preferred method-of preparation of the dyestuffs of thepresent invention, the disodium salt of 1-([2-alkoxy-5-alkyl-4-sulfophenyl] azo) -2-naphthol-6- sulfonic acid maybe prepared as follows: One part of a sulfanilic acid, corresponding tothe formula:

NHz

wherein R and R are each as above defined, is slurried in about 5 to 6parts, by weight, of water and dissolved by the addition of about 1.0 to1.2 parts, by weight, of 20 B. hydrochloric acid. The solution is cooledto about C. by the addition of ice. To this, there is added slowly about0.33 to 0.35 part of sodium nitrite (added as a 30% aqueous solution)and the mixture is agitated, at about 0 to C., for at least one hour.The resulting diazonium salt solution is added slowly to an alkalinesolution of Schaetfers salt (2-hydroxy-naphthalene-6-sodium sulfonate)consisting of about 1.1 parts of Sohaefiers salt, 8 parts of water and 1to 2 parts of sodium carbonate, the coupling solution being cooled toabout 10 C. with added ice. The resulting mixture which is alkaline toBrilliant Yellow indicator and which contains an excess of Schaefferssalt, is agitated for about 16 hours and then, after being heated toabout 65 to 70 C., is salted to about 5 to concentration by the additionof sodium chloride.

The mixture is agitated for about two to eight hours as it cools toambient temperature and the resulting slurry is filtered. The filtercake of the crude monoazo product is purified by dissolving it in about5 to 6 parts, by weight, of warm (55 C.) water and adding to thesolution about 0.5 part, by weight, of disodium phosphate. After beingagitated at 55 to 65 C. (for about 0.5 to 1 hour, about 0.25 to 1 part,by weight, of decolorizing charcoal and 0.25 to 1 part, by weight, of afilter aid is added and the mixture is filtered. The clarified filtrateis salted to precipitate the dyestuft as the disodium salt which isrecovered by filtration from the saline mother liquor. The filter cakemay be dried in conventional manner.

Other physiologically acceptable salts corresponding to above Formula Imay be prepared by known procedures. For example, the alkaline couplingmixture may be rendered acid with a mineral acid, such as hydrochloric,sulfuric or nitric acid, and potassium hydroxide may be added to theresultant acid mixture to cause precipitation of the correspondingpotassium salt; similarly, if ammonium hydroxide were to be addedinstead of potassium hydroxide at this stage, the corresponding ammoniumsalt would be obtained. Other physiologically acceptable salts maylikewise be obtained by adding a soluble salt, for example, calciumchloride, barium chloride, ferrous sulfate, to the alkaline couplingmixture to cause the corresponding calcium, barium or ferrous salt toprecipitate. The free acids, i.e., compounds of Formula I wherein M ishydrogen, are readily obtainable by neutralization of the alkalinecoupling mixture, for example, with a mineral acid, thereby causingprecipitation thereof from the neutralized coupling mixture; completeisolation of the free acids can be effected by extraction of the neutralto acid mass with a water-immiscible organic solvent, for example,diethylether, ethyl acetate, etc. and thereafter, evaporation of thesolvent from the extract.

The term edible substrata as used in this specification and the claimsappended hereto is intended to include a wide variety of food,pharmaceutical and cosmetic compositions. These may be in either solidor liquid form. Included also are wrappings and labels of various formscolored or printed thereon with inks containing these dyestuifs, whichmay come in contact with the material encased or labeled.

The addition of the dyestuffs of our invention to and incorporation inedible substrata is effected by methods well known in this art, forexample, by methods conventionally used with PD. & 0. Red No. 4, andhence, detailed discussion of this collateral aspect of our invention isdeemed unnecessary.

The following examples will serve to illustrate practice of theinvention but they are not intended to limit it to the details describedherein. Parts and percentages are by weight and temperatures are givenin degrees centigrade, unless otherwise specified.

EXAMPLE I To a slurry of 520 parts of S-methoxy-Z-methyl-sulfanilic acidin 3000 parts of water, 580 parts of 20 B. hydrochloric acid were added.The mixture was agitated for about /2 hour and the resulting solutionwas cooled to about 0 by the addition of ice. Then, 173 parts of sodiumnitrate, in the form of a aqueous solution, were added to the mass overa period of about hour while maintaining the solution at or below 5. Theresulting mixture thereafter was agitated for about one and one quarterhours to complete the diazotization reaction.

In a separate vessel, 591 parts of Schaefiers salt (2- naphthol-6-sodiumsulfonate) were slurried in 4000 parts of hot water and 600 parts ofsodium carbonate, as a 20% aqueous solution, were added thereto. Themixture was heated to 65 and the resultant solution was cooled first tobelow and then to about 10 by the addition of ice. The diazonium saltsolution prepared above was slowly (over a period of about one hour)added to the Schaeffers salt solution. The alkaline to Brilliant Yellowindicator coupling solution was agitated for about 16 hours and then washeated to between and After the addition of 1800 parts of lime freesodium chloride, the mixture was agitated for four hours as it graduallycooled to ambient temperature and the resultant precipitate which formedwas filtered from its mother liquor.

The filter cakes from two such couplings were combined and dissolved in10,000 parts of warm (55) water. To this solution 127 parts of anhydrousdisodium phosphate were added and the mass was agitated at 65 to for /2hour. After the addition of parts of decolorizing charcoal, the mass wasagitated for /2 hour and 120 parts of filter aid material were added.The mixture was agitated for one hour and then filtered. To theclarified filtrate, 1500 parts of lime free sodium chloride were addedslowly, and the mixture was agitated for about 16 hours to permit themass to cool and the purified monoazo dyestuif to precipitate. Theslurry was filtered and the filter cake was dried in a circulatory warmair oven. The solid product, the disodium salt of 1-([6-methoxy-4-sulfo-m-tolyl] azo -2-naphthol-6-sulfonic acid, corresponds tothe formula:

OCH: (1)11 dHa S O aNa EXAMPLE II The surprising solubility in water ofdyestuifs of the present invention is demonstrated by the following datawherein the solubility of the dyestuif prepared in Example I, above, wascompared at various temperatures with that of PD. & C. Red #4.

The latter has the formula:

SOaNa l S OaNa The tests were carried out as follows:

An excess quantity of the dyestuff was incrementally added to 25 partsof distilled water, shaking after each addition. The vessel was placedin a constant temperature bath maintained at a predeterminedtemperature. The resulting saturated solution was permitted to stand forseveral hours in the constant temperature bath and then filtered. A 5part aliquot of the filtered solution was evaporated to dryness in atared crucible at 130". From the weight of the residue, the solubilityof the dye in distilled water at the indicated temperature isdetermined. These comparative data are given in Table I below.

Temp. (deg) percent percent The significantly greater solubility inwater of the dyestufi of Example I compared to that of ED. & C. Red #4is surprising since both dyes have two solubilizing groups and are quitesimilar structurally and hence should possess a solubility character inthe same general area, as is indeed the fact when the solubility ofthese two dyestuffs is compared in 100% ethanol and 50% aqueous ethanolat 25, the solubility being, in each instance, trace and 1.3%respectively.

EXAMPLE III Maraschino cherries which had been dyed with ED. & C. Red #4and with the dyestuff prepared in Example I were stored for two monthsin light sugar syrup containing about 200 p.p.m. of S0 at ambienttemperature. The cherries were placed on white filter paper andexamined. Those dyed with FD. & C. Red #4 possessed a bright yellow-redshade and produced a slight red bleed on the filter paper. Thosecherries dyed with the dyestuff of this invention were slightly dullerin shade but yielded practically no bleed onto the white filter paper,indicating that it was superior in this respect to PD. & C. Red #4.

This characteristic was again demonstrated by placing half and wholecherries in contact with pear halves in light sugar syrup (such as isused in the conventional fruit cocktail preparation). After five daysthe fruits were examined. The pears stored with cherries dyed with PD. &C. Red #4 were colored a strong pink indicating that the dye had bledoff from the cherries. The pears stored with the cherries dyed withdyestuff of Example I were a yellow pink in shade indicating a light ontone yellow-pink bleed, which is generally more acceptable than theshade imparted by the RD. & C. Red #4.

It can thus be seen that valuable and highly desirable red monoazodyestufis which are substantially non-toxic to warm blooded animals andedible substrata colored therewith have been provided. The new dyestuffsare characterized also by surprisingly excellent solubility in water.

Our invention has been described and illustrated by reference tospecific embodiments thereof, and the examples illustrate the best modepresently known of carrying out the invention. It should be noted,however, that variations of these procedures are feasible and many suchvariations will be obvious to those skilled in this art in view of thedisclosures contained herein.

We claim:

1. A monoazo dyestuif having the formula SOaM wherein R and R are eachlower alkyl and M is hydrogen, ammonium or a physiologically acceptablemetal cation.

2. The monoazo dyestufi' of claim 1 wherein R is lower alkyl and R ismethyl.

3. The monoazo dyestuif of claim 1 wherein R is methyl and R is loweralkyl.

4. The monoazo dyestuff of claim 1 wherein R and R are each'methyl.

5. The monoazo dyestuif of claim 4 wherein M is an alkali metal.

6. The monoazo dyestuif of claim 4 wherein M is sodium.

7. The monoazo dyestuff of claim 4 wherein M is potassium.

8. The monoazo dyestufr" of claim 4 wherein M is ammonium.

9. The monoazo dyestutf of claim 4 wherein M is hydrogen.

References Cited UNITED STATES PATENTS 2,224,904 12/1940 Elley et al.44-9 3,046,141 7/1962 Long 260-197 CHARLES B. PARKER, Primary ExaminerC. F. WARREN, Assistant Examiner US. Cl. X.R.

32 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,5 9, 7 Dated Julv 7. 1970 Inventor) Gustav E. East and Russell I.Steiner It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

q Column 1, line 57, "barium calcium" should be barium, calcium-- Column1, line 59, "Formula I" should be Formula (I) Column 2, line 19,l([6-propoxyl-sulfo-m-tolyl]azo)-" should be l-([6propoxy-U-sulfomtolyl]azo)- Column 2, line 22, "l([2-methoxy-5-ethyl- I-sulfophenyl1"should be l-([2-methoxy-5ethyllsulfophenyl] Column 3, line 2, "Examplaryshould be --Exemplary;

Column 3, line 18, "Be. should be Be Column 3, line &6, "Formula I"should be Formula (I) Column 3, line 59, "Formula I" should be Formula(If) Column '4 line 1 4, "520" should be 521 Column line l5, "Be."should be Be Column 4 line 19, "nitrate" should be nitrite Column 2nd.formula (C.I #1 8700) should be inserted .to the right of formula.

Signed and sealed this 26th day of September 1972.

' (SEAL) .J

Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

